Tetravalent boron-containing proton-exchange solid supports and methods of making and using tetravalent boron-containing proton-exchange solid supports

ABSTRACT

A proton exchange solid support includes a porous polymer network including a polymer. The polymer includes a tetravalent boron-based acid group in a side chain of the polymer, and the tetravalent boron-based acid group includes a boron atom having a negative formal charge. A cation is ionically linked to the boron atom.

RELATED APPLICATIONS

The present application is a continuation application of U.S. Pat.Application No. 17/521,735, filed Nov. 8, 2021, which is a continuationof International Patent Application No. PCT/US2021/038956, filed Jun.24, 2021, which claims priority to U.S. Provisional Pat. Application No.63/109,943, filed Nov. 5, 2020, each of which is hereby incorporated byreference in its entirety. U.S. Pat. Application No. 17/521,735 is alsoa continuation-in-part of International Patent Application No.PCT/US2021/029705, filed Apr. 28, 2021, which also claims priority toU.S. Provisional Pat. Application No. 63/109,943, filed Nov. 5, 2020,each of which is hereby incorporated by reference in its entirety.

BACKGROUND INFORMATION

Proton-exchange solid supports may be used in proton exchange membranes(PEMs), which are semipermeable membranes that are engineered totransport protons (H⁺) while being impermeable to gases such as hydrogen(H₂) and oxygen (O₂). PEMs may be used in hydrogen fuel cells and waterelectrolysis systems under acidic conditions. PEMs may be composed of amechanically and chemically resistant particles and/or a porousframework with highly acidic functional groups. For example,Nafion-based proton exchange membranes contain a polytetrafluoroethylene(PTFE) porous structural framework with sulfonic acid groups. The easilydissociable sulfonic acid groups serve as proton transport agents in themembrane.

SUMMARY

The following description presents a simplified summary of one or moreaspects of the methods and systems described herein in order to providea basic understanding of such aspects. This summary is not an extensiveoverview of all contemplated aspects and is intended to neither identifykey or critical elements of all aspects nor delineate the scope of anyor all aspects. Its sole purpose is to present some concepts of one ormore aspects of the methods and systems described herein in a simplifiedform as a prelude to the more detailed description that is presentedbelow.

In some illustrative examples, a boron-containing proton-exchange solidsupport comprises a proton-exchange solid support comprising an oxygenatom and a tetravalent boron-based acid group comprising a boron atomcovalently bonded to the oxygen atom.

In some illustrative examples, a boron-containing proton-exchange solidsupport has general formula (Ia), (Ib), (Ic), or (Id):

wherein:

-   [SS] represents a solid support;

-   X¹ represents a substituent group having formula (IIa), (IIb),    (IIc), or (IId):

-   

-   

-   

-   

-   X² represents a group having formula (IIIa) or (IIb):

-   

-   

-   Y¹ and Y² are the same or different and each represent a tetravalent    boron-based acid group having formula (IV):

-   

-   where the boron (B) atom of formula (IV) is covalently bonded to the    oxygen (O) atom of X¹ or X², and Z¹, Z², and Z³ are the same or    different and each represents an alkyl group, an alkoxy group, an    alkyloxycarbonyl group, an aryl group, an aryloxy group, or a fluoro    group; and

-   R represents a C₁ to C₃₀ alkyl linker chain and optionally has one    or more pendant moieties, which may be the same or different for    each atom in the linker chain and which may comprise hydrogen, a    hydroxyl group, a fluoro group, a chloro group, a dialkylamino    group, a cyano group, a carboxylic acid group, a carboxylic amide    group, a carboxylic ester group, an alkyl group, an alkoxy group,    and an aryl group.

In some illustrative examples, a method of making a boron-containingproton-exchange solid support comprises modifying a proton-exchangesolid support with a tetravalent boron-based acid group.

In some illustrative examples, a membrane electrode assembly comprises acathode, an anode, and a proton exchange membrane positioned between thecathode and the anode, the proton exchange membrane comprising aproton-exchange solid support comprising an oxygen atom and atetravalent boron-based acid group comprising a boron atom covalentlybonded to the oxygen atom.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements.

FIG. 1A shows an illustrative configuration of a solid supportimplemented as a porous structural framework.

FIG. 1B shows another illustrative configuration of a solid supportimplemented as a solid support particle.

FIGS. 2A and 2B show illustrative reaction schemes for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a sulfur (S) atom through an oxygen (O)atom.

FIGS. 3A and 3B show illustrative reaction schemes for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a carbon (C) atom through an oxygen(O)atom.

FIGS. 4A and 4B show an illustrative reaction scheme for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a phosphorous (P) atom through anoxygen (O)atom.

FIGS. 5A and 5B show an illustrative reaction scheme for synthesizing aboron-containing proton-exchange solid support presenting twotetravalent boron-based acid groups linked to a phosphorous (P) atomthrough a single oxygen (O) atom.

FIGS. 6A and 6B show another illustrative reaction scheme forsynthesizing a boron-containing proton-exchange solid support presentinga tetravalent boron-based acid group linked to a phosphorous (P) atomthrough an oxygen (O)atom.

FIGS. 7A and 7B show another illustrative reaction scheme forsynthesizing a boron-containing proton-exchange solid support presentingtwo tetravalent boron-based acid groups linked to a phosphorous (P) atomthrough a single oxygen (O)atom.

FIGS. 8A and 8B show an illustrative reaction scheme for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to an oxygen (O) atom.

FIG. 9 shows an illustrative proton exchange membrane including a porousstructural framework including boron-based acid groups bonded to poresurfaces of the porous structural framework.

FIG. 10 shows an illustrative proton exchange membrane waterelectrolysis system incorporating a boron-containing porous membrane.

FIG. 11 shows an illustrative proton exchange membrane fuel cellincorporating a boron-containing porous membrane.

DETAILED DESCRIPTION

Herein described are tetravalent boron-containing proton-exchange solidsupports, apparatuses including tetravalent boron-containingproton-exchange solid supports, and methods of making and usingtetravalent boron-containing proton-exchange solid supports. In someexamples, a tetravalent boron-containing proton-exchange solid supportcomprises a proton-exchange solid support comprising an oxygen atom, anda tetravalent boron-based acid group comprising a boron atom covalentlybonded to the oxygen atom. In some examples, the boron-containingproton-exchange solid support further comprises a sulfur atom, a carbonatom, or a phosphorous atom covalently bonded to the oxygen atom. Theproton-exchange solid support may be formed of an amorphous orcrystalline inorganic material and/or a synthetic or natural polymer,and may be, for example, in the form of a porous polymer network, amicroparticle, or a nanoparticle.

The tetravalent boron-containing proton-exchange solid supportsdescribed herein are superacids with strong proton exchange properties.Electrically neutral boron has three valence electrons but can also forma tetravalent ion with a negative formal charge by covalently bondingwith four other atoms. Thus, the tetravalent boron-based acid groups areintrinsically ionic and may serve as proton transport agents. Thetetravalent boron-containing proton-exchange solid supports describedherein may be used in PEMs for water electrolysis and/or fuel cellapplications operating under acidic conditions. For example, inboron-containing PEMs described herein, cation (e.g., proton) exchangeis provided by protons ionically linked to the tetravalent, negativelycharged boron atoms. The presence of the oxygen-boron bonds increasesthe hydrophilicity of the boron-containing PEMs and stabilizes thenegatively charged boron atoms. The boron-containing PEMs describedherein also have high mechanical strength, high proton conductivity, lowelectron conductivity, chemical stability under a large pH gradient,durability, and low cost of production. In some examples, theboron-containing PEMs described herein also do not incorporate toxicmaterials. Implementations and uses of tetravalent boron-containingproton-exchange solid supports in PEMs will be described below in moredetail.

The tetravalent boron-containing proton-exchange solid supportsdescribed herein may also be used for filtering and/or neutralizingpathogens such as bacteria, viruses, and fungal spores. For example,tetravalent boron-containing proton-exchange porous membranes may beimplemented in face masks, surgical masks, air filters, and airpurification systems for enclosed spaces (e.g., homes, offices,hospitals, factories, vehicles, airplanes, etc.).

The compositions, apparatuses, and methods described herein may provideone or more of the benefits mentioned above and/or various additionaland/or alternative benefits that will be made apparent herein. Variousembodiments will now be described in more detail with reference to thefigures. It will be understood that the following embodiments are merelyillustrative and are not limiting, as various modifications may be madewithin the scope of the present disclosure.

An illustrative tetravalent boron-containing proton-exchange solidsupport comprises a proton-exchange solid support comprising a sulfuratom, a carbon atom, or a phosphorous atom covalently bonded to anoxygen atom, and one or more tetravalent boron-based acid groups eachcomprising a boron atom covalently bonded to the oxygen atom. Anillustrative tetravalent boron-containing proton-exchange solid supportmay have the general formula (Ia) or (Ib):

-   wherein [SS] represents a solid support; X is a substituent group    containing an oxygen (O) atom or a sulfur (S) atom, a carbon (C)    atom, or a phosphorous (P) atom covalently bonded to one or more    oxygen (O) atoms; and Y¹ and Y² each represent a tetravalent    boron-based acid group comprising a boron (B) atom covalently bonded    to the oxygen atom of substituent group X. As will be explained    below in more detail, substituent group X may be derived from a    precursor substituent group containing a hydroxyl group, such as a    hydroxyl group, an acid group (e.g., a phenol group or an oxoacid    such as a carboxylic acid group, a sulfonic acid group (e.g., a    sulfo group), a phosphonic acid group, or a phosphate group), or an    alcohol. Optionally, a tetravalent boron-containing proton-exchange    solid support may include a linker chain that links substituent    group X with solid support [SS]. For example, a tetravalent    boron-containing proton-exchange solid support may have the general    formula (Ic) or (Id):

-   

-   

-   where R represents a C₁ to C₃₀ alkyl linker chain and optionally has    one or more pendant moieties, which may be the same or different and    may each be independently selected from the group consisting of    hydrogen, a hydroxyl group, a fluoro group, a chloro group, a    dialkylamino group, a cyano group, a carboxylic acid group, a    carboxylic amide group, an ester group, an alkyl group, an alkoxy    group, and an aryl group.

Solid support [SS], substituent group X, and optionally linker chain R,in combination, are referred to herein as a proton-exchange solidsupport because this combination may be derived from a precursorproton-exchange solid support. For example, as will be explained belowin more detail, the proton-exchange solid support ([SS]-X or [SS]-R-X),prior to modification with tetravalent boron-based acid group Y¹ and/orY², may be a commercially-available ionomer (e.g., a sulfonicacid-functionalized PTFE) and may itself serve as a proton transportagent by dissociation of a precursor of substituent group X (e.g., acarboxylic acid group, a sulfonic acid group, a phosphonic acid group, aphosphate group, a phenol group, an alcohol group, or a hydroxyl group).

Solid support [SS] may be formed of any suitable material or combinationof materials, including inorganic materials and/or organic materials.Suitable inorganic materials may include amorphous inorganic materials(e.g., glass, fused silica, or ceramics) and/or crystalline inorganicmaterials (e.g., quartz, single crystal silicon, or alumina). Suitableorganic material may include, for example, synthetic and/or naturalpolymers (e.g., lignin, cellulose, chitin, etc.), ionomers, and thelike. In some examples, substituent group X is linked to a side chain ofsolid support [SS] or comprises a side chain of solid support [SS].

Solid support [SS] and/or the proton-exchange solid support of formulas(Ia)-(Id) (e.g., [SS]-X or [SS]-R-X) may have any suitable shape andform, such as a porous structural framework or a solid support particle.A porous structural framework may be, for example, a porous polymernetwork. FIG. 1A shows an illustrative configuration 100A of a porousstructural framework 102. As shown, a pore surface 104 adjacent to apore 106 is functionalized with a tetravalent boron-based acid group 108(e.g., Y¹ or Y²). While FIG. 1A shows only one tetravalent boron-basedacid group 108 bonded to pore surface 104, porous structural framework102 may have any other number and concentration of tetravalentboron-based acid groups 108 bonded to pore surface 104.

A solid support particle may include, for example, a microparticle, ananoparticle, and/or a resin bead. FIG. 1B shows an illustrativeconfiguration 100B in which the proton-exchange solid support offormulas (Ia)-(Id) (e.g., [SS]-X or [SS]-R-X) is implemented as a solidsupport particle 110. A boron-based acid group 112 is bonded to asurface 114 of solid support particle 110. In some examples (not shown),multiple solid support particles 110 may be linked together to form aporous structural framework (e.g., porous structural framework 102) withboron-based acid groups 112 bonded to pore surfaces (e.g., surfaces 114)within the porous structural framework.

Solid support particles 110 may be formed of any suitable material, suchas any material described above for porous structural framework 102,such as inorganic molecules (e.g., fused silica particles, ceramicparticles, etc.) or natural or synthetic organic molecules (e.g.,polymers). Solid support particles 110 may have any suitable shape andsize, ranging from tens of nanometers (nm) to hundreds of microns. Theporosity of a porous structural framework formed by solid supportparticles 110 may be controlled and defined by the size and/or shape ofsolid support particles 110. Solid support particles 110 may also beselected for their mechanical strength, their durability in anenvironment with a high pH gradient, and/or for their affinity to water(e.g., they may be chosen to be hydrophilic or hydrophobic depending onthe desired water-affinity balance).

Referring again to formulas (Ia) to (Id), substituent group X containsan oxygen (O)atom or a sulfur (S) atom, a carbon (C) atom, or aphosphorous (P) atom covalently bonded to one or more oxygen (O)atoms.In some examples, substituent group X is a derivative of a precursorsubstituent group containing a hydroxyl group, such as a pendanthydroxyl group linked to solid support [SS], a pendant acid group linkedto solid support [SS] (such as a sulfonic acid group, a sulfuric acidgroup, a carboxylic acid group, a carbonic acid group, a phosphonic acidgroup, a phosphoric acid group, or a phenol group), or an alcohol linkedto solid support [SS]. In some examples, substituent group X contains asulfur atom, a carbon atom, or a phosphorous atom covalently bonded toan oxygen atom and covalently bonded to an additional oxygen atom by adouble bond. Examples of substituent group X may include, withoutlimitation, an oxygen atom (O) (derived from a pendant hydroxyl group),a carboxylate ester (C(═O)O), a carbonate ester (OC(═O)O), a sulfonateester (S(═O)₂O), a sulfate ester (OS(═O)₂O), a phosphoryl group(P(═O)(OH)O or P(═O)O₂), and a phosphate group (OP(═O)O₂), an aryloxygroup (OAr) (e.g., phenoxy group), or an alkoxy group (OR). Furtherexamples of substituent group X are shown in the illustrative reactionschemes described below with reference to FIGS. 2A to 8B.

Tetravalent boron-containing acid groups Y¹ and Y² may be the same ordifferent and are represented by general formula (IV):

-   where the boron (B) atom is covalently bonded to the oxygen (O)atom    (not shown in formula IV) of substituent group X derived from the    precursor hydroxyl group. For example, when substituent X is a    derivative of a precursor acid group containing a sulfur (S) atom, a    carbon (C) atom, or a phosphorous (P) atom, the boron (B) atom is    covalently bonded to the oxygen (O) atom that is covalently bonded    to the sulfur (S) atom, carbon (C) atom, or phosphorous (P) atom of    substituent group X. Substituents Z¹, Z², and Z³ are the same or    different and each represents an alkyl group, an alkoxy group, an    alkyloxycarbonyl group, an aryl group, an aryloxy group, a hydroxyl    group, or a fluoro group. In some examples, groups Y¹ and/or Y² may    be an ester represented by formula (Va), (Vb), or (Vc):

-   

-   

-   

-   where R′, R″, and R‴ may be the same or different and may represent,    for example, an alkyl group, an alkoxy group, an alkyloxycarbonyl    group, an aryl group, or an aryloxy group. In yet further examples,    Y¹ and/or Y² are derived from boron trifluoride (i.e., Z¹, Z², and    Z³ are each a fluoro group (F)). Other examples of Y¹ and Y² are    shown and described in the illustrative reaction schemes described    below with reference to FIGS. 2A to 8B.

A tetravalent boron-containing proton-exchange solid support may besynthesized in any suitable way. In some examples, a tetravalentboron-containing proton-exchange solid support may be synthesized bycombining a proton-exchange solid support with boron trifluoride (BF₃)or a boron-based ester (e.g., a trivalent boron-based ester), as willnow be shown and described with reference to FIGS. 2A-8B. The followingreaction schemes are merely illustrative and are not limiting.

FIG. 2A shows an illustrative reaction scheme 200A for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a sulfur (S) atom through an oxygen (O)atom. As shown, a proton-exchange solid support 202 is modified withboron trifluoride 204 to produce boron-containing proton-exchange solidsupport 206. Boron trifluoride 204 may be used in the synthesis reactionin a diethyl ether and/or tetrahydrofuran complex. Boron trifluoride isa Lewis acid and is a stronger acid than boric acids and boronic acidsdue to the presence of three boron-fluorine bonds, with fluorine beingthe most electronegative element in the periodic table.

Proton-exchange solid support 202 includes a solid support 208, a linkerchain 210, and a sulfonic acid group 212. However, linker chain 210 isoptional and may be omitted in other examples. Solid support 208 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 202 comprises a sulfonicacid-functionalized polymer, such as a poyfluorosulfonic acid polymer, aperfluorinated sulfonic acid polymer, or a sulfonated PTFE basedfluoropolymer-copolymer. Examples of proton-exchange solid support 202may include, without limitation, ethanesulfonyl fluoride,2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-,with tetrafluoroethylene andtetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer. Commercially available sulfonic acid-functionalized polymersinclude, without limitation, Nafione® (available from E.I. Dupont deNemours and Company in various configurations and grades, includingNafion-H, Nafion HP Nafion 117, Nafion 115, Nafion 212, Nafion 211,Nafion NE1035, Nafion XL, etc.), Aquivion® (available from Solvay S.A.in different configurations and grades, including Aquivion® E98-05,Aquivion® PW98, Aquivion® PW87S, etc.), Gore-Select® (available fromW.L. Gore & Associates, Inc.), Flemion™ (available from Asahi GlassCompany), Pemion+™ (available from lonomr Innovations, Inc.), and anycombination, derivative, grade, or configuration thereof.

Linker chain 210 may be any suitable substituent group capable oflinking sulfonic acid group 212 to solid support 208. Linker chain 210may be implemented by any suitable linker chain, including any linkerchain described herein (e.g., linker chain R of formulas (Ia)-(Id)). Insome examples, linker chain 210 contains carbon, oxygen, and/ornitrogen. As shown in FIG. 2A, linker chain 210 is an alkyl chain oflength m, where m ranges from 1 to 30, and has one or more side groupsA, each of which may independently be hydrogen (H), a hydroxyl group(OH), a fluoro group (F), a chloro group (Cl), a dialkylamino group(NR₂, in which R may represent hydrogen or an organic combining group,such as a methyl group (CH₃)), a cyano group (CN), a carboxylic acid(COOH) group, a carboxylic amide group, an ester group, an alkyl group,an alkoxy group, and an aryl group.

In some examples, boron trifluoride 204 and sulfonic acid group 212 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 206 includes aproton-exchange solid support 214 comprising a sulfur atom covalentlybonded to an oxygen atom, and a tetravalent boron-based acid group 216comprising a boron atom covalently bonded to the oxygen atom.Boron-containing proton-exchange solid support 206 is a superacid withstrong proton exchange properties. As mentioned above, electricallyneutral boron has three valence electrons but can also form atetravalent ion with a negative formal charge by covalently bonding withfour other atoms, as shown in FIG. 2B. Thus, tetravalent boron-basedacid group 216 is intrinsically ionic and may serve as a protontransport agent.

FIG. 2B shows another illustrative reaction scheme 200B for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to a sulfur (S) atom throughan oxygen (O) atom. Reaction scheme 200B is similar to reaction scheme200A except that in reaction scheme 200B proton-exchange solid support202 is combined with a boron-based ester 218 instead of with borontrifluoride 204. Boron-based ester 218 may be a borate ester or aboronic ester (also referred to as a boronate ester). A borate ester maybe derived, for example, by reacting boric acid (B(OH)₃) or a relatedboron oxide with an alcohol (ROH) in the presence of heat. A boronicester may be derived, for example, by reacting a boronic acid or arelated boron oxide with an alcohol (ROH) in the presence of heat. Thus,in boron-based ester 218 of FIG. 2B, groups X, Y, and Z may eachindependently represent an alkoxy group (OR), an aryloxy group (OAr), analkyl group (R), an aryl group (Ar), or a fluoro group (F), with theproviso that at least two of X, Y, and Z includes an oxygen atom bondedto the boron atom to thereby form a boron-based ester. Examples of aboron-based ester may include, without limitation, trimethyl borate,triethyl borate, tributyl borate, n-octyl borate, tridecyl borate,tritetradecyl borate, triisopropyl borate, tris(hexafluoroisopropyl)borate, trimethoxycyclotriboroxane, triphenyl borate, tri-o-tolylborate, tris(trimethylsilyl) borate, tetraacetyl diborate,tris(2,2,2-trifluoroethyl) borate, bis-pinacol diboronate, pinacolboronate, allylboronic acid pinacol ester, and diisopropoxymethylborane.

In some examples, boron-based ester 218 and sulfonic acid group 212 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 220 includesproton-exchange solid support 214 comprising a sulfur atom covalentlybonded to an oxygen atom, and a tetravalent boron-based acid group 222comprising a boron atom covalently bonded to the oxygen atom. Likeboron-containing proton-exchange solid support 206, boron-containingproton-exchange solid support 220 is a superacid with strong protonexchange properties and is intrinsically ionic.

FIG. 3A shows an illustrative reaction scheme 300A for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a carbon (C) atom through an oxygen (O)atom. As shown, a proton-exchange solid support 302 is modified withboron trifluoride 304 to produce boron-containing proton-exchange solidsupport 306. Boron trifluoride may be used in the synthesis reaction ina diethyl ether and/or tetrahydrofuran complex.

Proton-exchange solid support 302 includes a solid support 308, a linkerchain 310, and a carboxylic acid group 312. However, linker chain 310 isoptional and may be omitted in other examples. Solid support 308 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 302 comprises a carboxylicacid-functionalized polymer, such as a polyacrylic acid polymer.

Linker chain 310 may be any suitable substituent group capable oflinking carboxylic acid group 312 to solid support 308. Linker chain 310may be implemented by any suitable linker chain, including any linkerchain described herein (e.g., linker chain R of formulas (Ia)-(Id)).Linker chain 310 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 304 and carboxylic acid group 312are combined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 306 includes aproton-exchange solid support 314 comprising a carbon atom covalentlybonded to an oxygen atom, and a tetravalent boron-based acid group 316comprising a boron atom covalently bonded to the oxygen atom.Boron-containing proton-exchange solid support 306 is a superacid withstrong proton exchange properties and is intrinsically ionic.

FIG. 3B shows another illustrative reaction scheme 300B for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to a carbon (C) atom throughan oxygen (O) atom. Reaction scheme 300B is similar to reaction scheme300A except that in reaction scheme 300B proton-exchange solid support302 is combined with a boron-based ester 318 instead of with borontrifluoride 304. Boron-based ester 318 may be the same as or similar toboron-based ester 218.

In some examples, boron-based ester 318 and carboxylic acid group 312are combined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 320 includesproton-exchange solid support 314 comprising a carbon atom covalentlybonded to an oxygen atom, and a tetravalent boron-based acid group 322comprising a boron atom covalently bonded to the oxygen atom. Likeboron-containing proton-exchange solid support 306, boron-containingproton-exchange solid support 320 is a superacid with strong protonexchange properties and is intrinsically ionic.

FIG. 4A shows an illustrative reaction scheme 400A for synthesizing aboron-containing proton-exchange solid support presenting a tetravalentboron-based acid group linked to a phosphorous (P) atom through anoxygen (O) atom. As shown, a proton-exchange solid support 402 ismodified with boron trifluoride 404 to produce boron-containingproton-exchange solid support 406. Boron trifluoride may be used in thesynthesis reaction in a diethyl ether and/or tetrahydrofuran complex.

Proton-exchange solid support 402 includes a solid support 408, a linkerchain 410, and a phosphonic acid group 412. However, linker chain 410 isoptional and may be omitted in other examples. Solid support 408 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 402 comprises a phosphonicacid-functionalized polymer, such as a polyvinylphosphonic acid (PVPA)polymer.

Linker chain 410 may be any suitable substituent group capable oflinking phosphonic acid group 412 to solid support 408. Linker chain 410may be implemented by any suitable linker chain, including any linkerchain described herein (e.g., linker chain R of formulas (Ia)-(Id)).Linker chain 410 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 404 and phosphonic acid group 412are combined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 406 includes aproton-exchange solid support 414 comprising a phosphorous atomcovalently bonded to an oxygen atom, and a tetravalent boron-based acidgroup 416 comprising a boron atom covalently bonded to the oxygen atom.Boron-containing proton-exchange solid support 406 is a superacid withstrong proton exchange properties and is intrinsically ionic.

FIG. 4B shows another illustrative reaction scheme 400B for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to a phosphorous (P) atomthrough an oxygen (O) atom. Reaction scheme 400B is similar to reactionscheme 400A except that in reaction scheme 400B proton-exchange solidsupport 402 is combined with a boron-based ester 418 instead of withboron trifluoride 404. Boron-based ester 418 may be the same as orsimilar to boron-based ester 218.

In some examples, boron-based ester 418 and phosphonic acid group 412are combined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 420 includesproton-exchange solid support 414 comprising a phosphorous atomcovalently bonded to an oxygen atom, and a tetravalent boron-based acidgroup 422 comprising a boron atom covalently bonded to the oxygen atom.Like boron-containing proton-exchange solid support 406,boron-containing proton-exchange solid support 420 is a superacid withstrong proton exchange properties and is intrinsically ionic.

FIG. 5A shows an illustrative reaction scheme 500A for synthesizing aboron-containing proton-exchange solid support presenting twotetravalent boron-based acid groups each linked to the same phosphorous(P) atom through different oxygen (O) atoms. As shown, a proton-exchangesolid support 502 is modified with boron trifluoride 504 to produceboron-containing proton-exchange solid support 506. Boron trifluoridemay be used in the synthesis reaction in a diethyl ether and/ortetrahydrofuran complex.

Proton-exchange solid support 502 includes a solid support 508, a linkerchain 510, and a phosphonic acid group 512. However, linker chain 510 isoptional and may be omitted in other examples. Solid support 508 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 502 comprises a phosphonicacid-functionalized polymer, such as PVPA polymer.

Linker chain 510 may be any suitable substituent group capable oflinking phosphonic acid group 512 to solid support 508. Linker chain 510may be implemented by any suitable linker chain, including any linkerchain described herein (e.g., linker chain R of formulas (Ia)-(Id)).Linker chain 510 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 504 and phosphonic acid group 512are combined in approximately a two-to-one (2:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 506 includes aproton-exchange solid support 514 comprising a phosphorous atom and twotetravalent boron-based acid groups 516-1 and 516-2 each comprising aboron atom covalently bonded to different oxygen atoms ofproton-exchange solid support 506 (e.g., to different oxygen atoms ofphosphonic acid group 512). Boron-containing proton-exchange solidsupport 506 is a superacid with strong proton exchange properties and isintrinsically ionic.

FIG. 5B shows another illustrative reaction scheme 500B for synthesizinga boron-containing proton-exchange solid support presenting twotetravalent boron-based acid groups each linked to the same phosphorous(P) atom through two different oxygen (O) atoms. Reaction scheme 500B issimilar to reaction scheme 500A except that in reaction scheme 500Bproton-exchange solid support 502 is combined with a boron-based ester518 instead of with boron trifluoride 504. Boron-based ester 518 may bethe same as or similar to boron-based ester 218.

In some examples, boron-based ester 518 and phosphonic acid group 512are combined in approximately a two-to-one (2:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 520 includesproton-exchange solid support 514 comprising a phosphorous atom and twotetravalent boron-based acid groups 522-1 and 522-2 each comprising aboron atom covalently bonded to different oxygen atoms ofproton-exchange solid support 520 (e.g., to different oxygen atoms ofphosphonic acid group 512). Boron-containing proton-exchange solidsupport 506 is a superacid with strong proton exchange properties and isintrinsically ionic.

FIG. 6A shows another illustrative reaction scheme 600A for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to a phosphorous (P) atomthrough an oxygen (O) atom. As shown, a proton-exchange solid support602 is modified with boron trifluoride 604 to produce boron-containingproton-exchange solid support 606. Boron trifluoride may be used in thesynthesis reaction in a diethyl ether and/or tetrahydrofuran complex.

Proton-exchange solid support 602 includes a solid support 608, a linkerchain 610, and a monophosphate group 612. However, linker chain 610 isoptional and may be omitted in other examples. Solid support 408 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 602 comprises a phosphate-functionalizedpolymer, such as a polybenzimidazole (PBI) doped with phosphoric acid.

Linker chain 610 may be any suitable substituent group capable oflinking phosphate group 612 to solid support 608. Linker chain 610 maybe implemented by any suitable linker chain, including any linker chaindescribed herein (e.g., linker chain R of formulas (Ia)-(Id)). Linkerchain 610 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 604 and phosphate group 612 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 606 includes aproton-exchange solid support 614 comprising a phosphorous atomcovalently bonded to an oxygen atom and a tetravalent boron-based acidgroup 616 comprising a boron atom covalently bonded to the oxygen atom.Boron-containing proton-exchange solid support 606 is a superacid withstrong proton exchange properties and is intrinsically ionic.

The resulting boron-containing proton-exchange solid support 606includes a proton-exchange solid support 614 comprising a phosphorousatom covalently bonded to an oxygen atom, and a tetravalent boron-basedacid group 616 comprising a boron atom covalently bonded to the oxygenatom. Boron-containing proton-exchange solid support 606 is a superacidwith strong proton exchange properties and is intrinsically ionic.

FIG. 6B shows another illustrative reaction scheme 600B for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to a phosphorous (P) atomthrough an oxygen (O) atom. Reaction scheme 600B is similar to reactionscheme 600A except that in reaction scheme 600B proton-exchange solidsupport 602 is combined with a boron-based ester 618 instead of withboron trifluoride 604. Boron-based ester 618 may be the same as orsimilar to boron-based ester 218.

In some examples, boron-based ester 618 and phosphate group 612 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 620 includesproton-exchange solid support 614 comprising a phosphorous atomcovalently bonded to an oxygen atom, and a tetravalent boron-based acidgroup 622 comprising a boron atom covalently bonded to the oxygen atom.Like boron-containing proton-exchange solid support 606,boron-containing proton-exchange solid support 620 is a superacid withstrong proton exchange properties and is intrinsically ionic.

FIG. 7A shows an illustrative reaction scheme 700A for synthesizing aboron-containing proton-exchange solid support presenting twotetravalent boron-based acid groups each linked to the same phosphorous(P) atom through different oxygen (O) atoms. As shown, aphosphate-functionalized proton-exchange solid support 702 is modifiedwith boron trifluoride 704 to produce boron-containing proton-exchangesolid support 706. Boron trifluoride may be used in the synthesisreaction in a diethyl ether and/or tetrahydrofuran complex.

Proton-exchange solid support 702 includes a solid support 708, a linkerchain 710, and a phosphate group 712. However, linker chain 710 isoptional and may be omitted in other examples. Solid support 708 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 702 comprises a phosphate-functionalizedpolymer, such as a PBI polymer.

Linker chain 710 may be any suitable substituent group capable oflinking phosphate group 712 to solid support 708. Linker chain 710 maybe implemented by any suitable linker chain, including any linker chaindescribed herein (e.g., linker chain R of formulas (Ia)-(Id)). Linkerchain 710 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 704 and phosphate group 712 arecombined in approximately a two-to-one (2:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 706 includes aproton-exchange solid support 714 comprising a phosphorous atom and twotetravalent boron-based acid groups 716-1 and 716-2 each comprising aboron atom covalently bonded to different oxygen atoms ofproton-exchange solid support 706 (e.g., to different oxygen atoms ofphosphate group 712). Boron-containing proton-exchange solid support 706is a superacid with strong proton exchange properties and isintrinsically ionic.

FIG. 7B shows another illustrative reaction scheme 700B for synthesizinga boron-containing proton-exchange solid support presenting twotetravalent boron-based acid groups linked to a phosphorous (P) atomthrough a single oxygen (O) atom. Reaction scheme 700B is similar toreaction scheme 700A except that in reaction scheme 700B proton-exchangesolid support 702 is combined with a boron-based ester 718 instead ofwith boron trifluoride 704. Boron-based ester 718 may be the same as orsimilar to boron-based ester 218.

In some examples, boron-based ester 718 and phosphate group 712 arecombined in approximately a two-to-one (2:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 520 includesproton-exchange solid support 714 comprising a phosphorous atom and twotetravalent boron-based acid groups 722-1 and 722-2 each comprising aboron atom covalently bonded to different oxygen atoms ofproton-exchange solid support 720 (e.g., to different oxygen atoms ofphosphonic acid group 712). Boron-containing proton-exchange solidsupport 706 is a superacid with strong proton exchange properties and isintrinsically ionic.

FIG. 8A shows another illustrative reaction scheme 800A for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to an oxygen atom. As shown, aproton-exchange solid support 802 is modified with boron trifluoride 804to produce boron-containing proton-exchange solid support 806. Borontrifluoride may be used in the synthesis reaction in a diethyl etherand/or tetrahydrofuran complex.

Proton-exchange solid support 802 includes a solid support 808, a linkerchain 810, and a hydroxyl group 812. However, linker chain 810 isoptional and may be omitted in other examples. Solid support 808 may beimplemented by any suitable solid support, including any solid supportdescribed herein (e.g., solid support [SS] of formulas (Ia)-(Id)) andmay be implemented in any suitable form, including as a porousstructural framework (e.g., porous structural framework 102) or a solidsupport particle (e.g., solid support particle 110). In some examples,proton-exchange solid support 802 comprises a natural polymer presentinga pendant hydroxyl group, such as lignin, cellulose, or chitin.

Linker chain 810 may be any suitable substituent group capable oflinking hydroxyl group 812 to solid support 808. Linker chain 810 may beimplemented by any suitable linker chain, including any linker chaindescribed herein (e.g., linker chain R of formulas (Ia)-(Id)). Linkerchain 810 may be the same as or similar to linker chain 210.

In some examples, boron trifluoride 804 and hydroxyl group 812 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 806 includes aproton-exchange solid support 814 comprising a an oxygen atom derivedfrom hydroxyl group 812, and a tetravalent boron-based acid group 816comprising a boron atom covalently bonded to the oxygen atom.Boron-containing proton-exchange solid support 806 is a superacid withstrong proton exchange properties and is intrinsically ionic.

FIG. 8B shows another illustrative reaction scheme 800B for synthesizinga boron-containing proton-exchange solid support presenting atetravalent boron-based acid group linked to an oxygen (O) atom.Reaction scheme 800B is similar to reaction scheme 800A except that inreaction scheme 800B proton-exchange solid support 802 is combined witha boron-based ester 818 instead of with boron trifluoride 804.Boron-based ester 818 may be the same as or similar to boron-based ester218.

In some examples, boron-based ester 818 and hydroxyl group 812 arecombined in approximately a one-to-one (1:1) stoichiometric ratio,although they may be combined in any other suitable ratio. The resultingboron-containing proton-exchange solid support 820 includesproton-exchange solid support 814 comprising an oxygen atom, and atetravalent boron-based acid group 822 comprising a boron atomcovalently bonded to the oxygen atom. Like boron-containingproton-exchange solid support 806, boron-containing proton-exchangesolid support 820 is a superacid with strong proton exchange propertiesand is intrinsically ionic.

Reaction schemes 200A-800B may be used to modify a component of a PEM,including dopants, nanoparticles, microparticles, and ionomers, as wellas to modify commercially available polymers and ionomers or PEMs havinga pendant hydroxyl group (e.g., from a sulfonic acid group, a carboxylicacid group, a phosphonic acid group, a phosphate group, a phenol group,an alcohol, or a pendant hydroxyl group) with a tetravalent boron-basedacid group. Ionomers generally include the class of polymeric materialshaving a pendant acid group. Therefore, when the solid support (e.g.,solid support 208, optionally with linker chain 210) is a polymer andcomprises a pendant acid group, a precursor proton-exchange solidsupport (e.g., proton-exchange solid support 202) is an ionomer due tothe presence of the pending acid group (e.g., sulfonic acid group 212),as is the resulting boron-containing proton-exchange solid support(e.g., boron-containing proton-exchange solid support 206 or 220) due tothe pending boron-based acid group (e.g., boron-based acid group 216 or222). When the boron-containing proton-exchange solid support is anionomer, a PEM may be formed by extruding or gel casting theboron-containing proton exchange solid support (e.g., boron-containingproton-exchange solid support 206 or 220). Catalyst coated membranes mayalso be formulated using the ionomer form of the boron-containingproton-exchange solid support as a binder for holding catalysts on bothsides of the PEM.

The boron-containing proton-exchange solid supports described herein maybe used in water electrolysis and/or fuel cell applications.Illustrative applications will now be described with reference to FIGS.9-11 .

In some examples, tetravalent boron-containing proton-exchange solidsupports may be used in a PEM. FIG. 9 shows an illustrative protonexchange membrane 900 (PEM 900). PEM 900 includes a porous structuralframework 902 and tetravalent boron-based acid groups 904 distributedthroughout porous structural framework 902 and bonded to pore surfacesof porous structural framework 902.

Porous structural framework 902 may be formed of any suitable solidsupport or combination of solid supports described herein, includinginorganic materials and/or organic materials. Suitable inorganicmaterials may include amorphous inorganic materials (e.g., glass, fusedsilica, or ceramics) and/or crystalline inorganic materials (e.g.,quartz, single crystal silicon, or alumina). Suitable organic materialmay include, for example, synthetic and/or natural polymers (e.g.,cellulose).

PEM 900 may have a thickness d ranging from a few microns to hundreds ofmicrons. With the configurations described herein, PEM 900 may withstandpressure differentials of up to 30 atmospheres and acidic pH gradientsacross the membrane. PEM 900 may also be permeable to water and protons,which may be conducted through PEM 900 as indicated by arrow 906, butPEM 900 is generally impermeable to gases including hydrogen and oxygen.

FIG. 10 shows an illustrative proton exchange membrane waterelectrolysis system 1000 (PEM water electrolysis system 1000)incorporating a boron-containing porous membrane. PEM water electrolysissystem 1000 uses electricity to split water into oxygen (O₂) andhydrogen (H₂) via an electrochemical reaction. The configuration of PEMwater electrolysis system 1000 is merely illustrative and not limiting,as other suitable configurations as well as other suitable waterelectrolysis systems may incorporate a boron-containing porous membrane.

As shown in FIG. 10 , PEM water electrolysis system 1000 includes amembrane electrode assembly 1002 (MEA 1002), porous transport layers1004-1 and 1004-2, bipolar plates 1006-1 and 1006-2, and an electricalpower supply 1008. PEM water electrolysis system 1000 may also includeadditional or alternative components not shown in FIG. 10 as may serve aparticular implementation.

MEA 1002 includes a PEM 1010 positioned between a first catalyst layer1012-1 and a second catalyst layer 1012-2. PEM 1010 electricallyisolates first catalyst layer 1012-1 from second catalyst layer 1012-2while providing selective conductivity of cations, such as protons (H⁺),and while being impermeable to gases such as hydrogen and oxygen. PEM1010 may be implemented by any suitable PEM. For example, PEM 1010 maybe implemented by a boron-containing porous membrane (e.g., PEM 900)comprising a porous structural framework with tetravalent boron-basedacid groups bonded to pore surfaces within the porous structuralframework.

First catalyst layer 1012-1 and second catalyst layer 1012-2 areelectrically conductive electrodes with embedded electrochemicalcatalysts (not shown), such as platinum, ruthenium, and/or or cerium(IV)oxide. In some examples, first catalyst layer 1012-1 and second catalystlayer 1012-2 are formed using an ionomer to bind catalyst nanoparticles.The ionomer used to form first catalyst layer 1012-1 and second catalystlayer 1012-2 may include a tetravalent boron-containing proton-exchangesolid support as described herein.

MEA 1002 is placed between porous transport layers 1004-1 and 1004-2,which are in turn placed between bipolar plates 1006-1 and 1006-2 withflow channels 1014-1 and 1014-2 located in between bipolar plates 1006and porous transport layers 1004.

In MEA 1002, first catalyst layer 1012-1 functions as an anode andsecond catalyst layer 1012-2 functions as a cathode. When PEM waterelectrolysis system 1000 is powered by power supply 1008, an oxygenevolution reaction (OER) occurs at anode 1012-1, represented by thefollowing electrochemical half-reaction:

Protons are conducted from anode 1012-1 to cathode 1012-2 through PEM1010, and electrons are conducted from anode 1012-1 to cathode 1012-2 byconductive path around PEM 1010. PEM 1010 allows for the transport ofprotons (H⁺) and water from the anode 1012-1 to the cathode 1012-2 butis impermeable to oxygen and hydrogen. At cathode 1012-2, the protonscombine with the electrons in a hydrogen evolution reaction (HER),represented by the following electrochemical half-reaction:

The OER and HER are two complementary electrochemical reactions forsplitting water by electrolysis, represented by the following overallwater electrolysis reaction:

FIG. 11 shows an illustrative proton exchange membrane fuel cell 1100(PEM fuel cell 1100) including a boron-containing porous membrane. PEMfuel cell 1100 produces electricity as a result of electrochemicalreactions. In this example, the electrochemical reactions involvereacting hydrogen gas (H₂) and oxygen gas (O₂) to produce water andelectricity. The configuration of PEM fuel cell 1100 is merelyillustrative and not limiting, as other suitable configurations as wellas other suitable proton exchange membrane fuel cells may incorporate aboron-containing porous membrane.

As shown in FIG. 11 , PEM fuel cell 1100 includes a membrane electrodeassembly 1102 (MEA 1102), porous transport layers 1104-1 and 1104-2,bipolar plates 1106-1 and 1106-2. An electrical load 1108 may beelectrically connected to MEA 1102 and driven by PEM fuel cell 1100. PEMfuel cell 1100 may also include additional or alternative components notshown in FIG. 11 as may serve a particular implementation.

MEA 1102 includes a PEM 1110 positioned between a first catalyst layer1112-1 and a second catalyst layer 1112-2. PEM 1110 electricallyisolates first catalyst layer 1112-1 from second catalyst layer 1112-2while providing selective conductivity of cations, such as protons (H⁺),and while being impermeable to gases such as hydrogen and oxygen. PEM1110 may be implemented by any suitable PEM. For example, PEM 1110 maybe implemented by a boron-containing porous membrane (e.g., PEM 900)comprising a porous structural framework with boron-based acid groupsbonded to pore surfaces within the porous structural framework.

First catalyst layer 1112-1 and second catalyst layer 1112-2 areelectrically conductive electrodes with embedded electrochemicalcatalysts (not shown). In some examples, first catalyst layer 1112-1 andsecond catalyst layer 1112-2 are formed using an ionomer to bindcatalyst nanoparticles. In some examples, the ionomer used to form firstcatalyst layer 1112-1 and second catalyst layer 1104-2 includes anionomer incorporating a tetravalent boron-containing proton-exchangesolid support as described herein.

MEA 1102 is placed between porous transport layers 1104-1 and 1104-2,which are in turn placed between bipolar plates 1106-1 and 1106-2 withflow channels 1114 located in between. In MEA 1102, first catalyst layer1112-1 functions as a cathode and second catalyst layer 1112-2 functionsas an anode. Cathode 1112-1 and anode 1112-2 are electrically connectedto load 1108, and electricity generated by PEM fuel cell 1100 drivesload 1108.

During operation of PEM fuel cell 1100, hydrogen gas (H₂) flows into theanode side of PEM fuel cell 1100 and oxygen gas (O₂) flows into thecathode side of PEM fuel cell 1100. At anode 1112-2, hydrogen moleculesare catalytically split into protons (H⁺) and electrons (e⁻) accordingto the following hydrogen oxidation reaction (HOR):

The protons are conducted from anode 1112-2 to cathode 1112-1 throughPEM 1100, and the electrons are conducted from anode 1112-2 to cathode1112-1 around PEM 1110 through a conductive path and load 1108. Atcathode 1112-1, the protons and electrons combine with the oxygen gasaccording to the following oxygen reduction reaction (ORR):

Thus, the overall electrochemical reaction for the PEM fuel cell 1100is:

In the overall reaction, PEM fuel cell 1100 produces water at cathode1112-1. Water may flow from cathode 1112-1 to anode 1112-2 through PEM1110 and may be removed through outlets at the cathode side and/or anodeside of PEM fuel cell 1100. The overall reaction generates electrons atthe anode that drive load 1108.

The tetravalent boron-containing proton-exchange solid supportsdescribed herein (incorporated as a porous structural framework (e.g.,PEM 900) or as solid support particles) may also be used as apathogen-neutralizing porous membrane. For example, porous structuralframework 902 may have pores that are small enough to prevent thepassage of pathogens such as bacteria, fungal spores, and viruses. Theboron-based acid groups 904 may also have antipathogenic activityagainst bacteria, fungi, and viruses, including SARS-CoV-2. For example,the basic protein sites of pathogens, including SARS-CoV-2, mayionically bond with the acidic boron sites of the proton exchangemembranes, thereby preventing passage of the pathogens through theproton exchange membranes. As a result, the proton exchange membranesmay be implemented in face masks, surgical masks, and air filters andair purification systems for enclosed spaces (e.g., homes, offices,hospitals, factories, vehicles, airplanes, etc.).

In the preceding description, various illustrative embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the claims that follow. For example, certain features ofone embodiment described herein may be combined with or substituted forfeatures of another embodiment described herein. The description anddrawings are accordingly to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. A proton-exchange solid support comprising: aporous polymer network comprising a polymer, wherein: the polymercomprises a tetravalent boron-based acid group in a side chain of thepolymer; and the tetravalent boron-based acid group comprises a boronatom having a negative formal charge; and a cation ionically linked tothe boron atom.
 2. The proton-exchange solid support of claim 1, whereinthe side chain of the polymer comprises an alkyl chain of length m,where m ranges from one (1) to thirty (30), and wherein the alkyl chainis substituted or unsubstituted.
 3. The proton-exchange solid support ofclaim 1, wherein the tetravalent boron-based acid group is located at apore surface of the porous polymer network.
 4. The proton-exchange solidsupport of claim 1, wherein the tetravalent boron-based acid group hasthe general formula OBF₃ where O is an oxygen atom included in the sidechain of the polymer and B is the boron atom.
 5. The proton-exchangesolid support of claim 1, wherein the tetravalent boron-based acid grouphas the general formula (O)B(Z¹)(Z²)(Z³) where O is an oxygen atomincluded in the side chain of the polymer, B is the boron atom, and Z¹,Z², and Z³ are the same or different and each represents an alkyl group,an alkoxy group, an alkyloxycarbonyl group, an aryl group, an aryloxygroup, or a fluoro group.
 6. The proton-exchange solid support of claim5, wherein the boron atom is covalently bonded to at least one atomother than oxygen.
 7. A method of making a proton-exchange solidsupport, comprising: modifying a side chain of a polymer of a porouspolymer network with a tetravalent boron-based acid group, wherein thetetravalent boron-based acid group comprises a boron atom covalentlybonded to four atoms and having a negative formal charge; and ionicallylinking a cation to the boron atom.
 8. The method of claim 7, wherein:the polymer comprises a pendant hydroxyl group in the side chain of thepolymer; and modifying the side chain of the polymer comprises combiningboron trifluoride or a trivalent boron-based ester with the pendanthydroxyl group.
 9. The method of claim 7, wherein the side chain of thepolymer comprises an alkyl chain of length m, where m ranges from one(1) to thirty (30), and wherein the alkyl chain is substituted orunsubstituted.
 10. The method of claim 7, wherein the tetravalentboron-based acid group has the general formula (O)B(Z¹)(Z²)(Z³) where Ois an oxygen atom included in the side chain of the polymer, B is theboron atom, and Z¹, Z², and Z³ are the same or different and eachrepresents an alkyl group, an alkoxy group, an alkyloxycarbonyl group,an aryl group, an aryloxy group, or a fluoro group.
 11. The method ofclaim 7, wherein the boron atom is covalently bonded to at least oneatom other than oxygen.
 12. The method of claim 7, wherein the polymercomprises an ionomer.
 13. The method of claim 7, wherein the polymercomprises a sulfonic acid-functionalized polymer.
 14. The method ofclaim 7, wherein the proton-exchange solid support comprises acarboxylic acid-functionalized polymer.
 15. The method of claim 7,wherein the proton-exchange solid support comprises a phosphonicacid-functionalized polymer.
 16. The method of claim 15, wherein thephosphonic acid-functionalized polymer comprises a polyvinylphosphonicacid polymer.
 17. The method of claim 7, wherein the proton-exchangesolid support comprises a phosphate-functionalized polymer.
 18. Themethod of claim 17, wherein the phosphate-functionalized polymercomprises a polybenzimidazole polymer doped with phosphoric acid.
 19. Aproton-exchange solid support comprising: a porous polymer networkcomprising a polymer, wherein: the polymer comprises a tetravalentboron-based acid group in a side chain of the polymer; and thetetravalent boron-based acid group comprises a boron atom having anegative formal charge.
 20. The proton-exchange solid support of claim19, wherein the side chain of the polymer comprises an alkyl chain oflength m, where m ranges from one (1) to thirty (30), and wherein thealkyl chain is substituted or unsubstituted.